The inadequate treatment of municipal solid waste which is being put in landfills and the increasing addition of nondegradable materials, including plastics, to the municipal solid waste streams are combining to reduce drastically the number of landfills available and to increase the costs of municipal solid waste disposal. While the recycling of reusable components of the waste stream is desirable in many instances, there are some products which do not readily fit into this framework, e.g. disposable personal absorbents such as diapers and sanitary napkins, garbage bags, and numerous other products. The composting of non-recyclable solid waste is a recognized and growing method of reducing solid waste volume for landfilling and/or making a useful product from the waste to improve the fertility of fields and gardens. One of the limitations to marketing such compost is the visible contamination by undegraded plastic such as film and fiber fragments.
As related in the aforesaid parent application, Tietz was faced with several objectives, as follows:
1 --to provide components which are useful in disposable products and which are degraded into less contaminating forms under the conditions typically existing in waste composting processes. These conditions may involve temperatures no higher than 70.degree. C., and averaging more nearly 55.degree. C.-60.degree. C., humid conditions as high as 100% relative humidity, and exposure times which range from two weeks to more than three months.
2 --to provide disposable components which will not only degrade aerobically in composting, but will continue to degrade in the soil or landfill anaerobically. As long as water is present, they will continue to break down into low molecular weight fragments which can be ultimately biodegraded by microorganisms completely into biogas, biomass and liquid leachate, as for natural organics like wood.
3 --to provide novel polyesters for making the aforementioned fibers, films, coatings and nonwoven sheets of the polyesters, and disposable diapers containing the nonwoven sheets.
4 --to provide polyesters and derivative products which have low ingredient costs and yet provide strength and toughness properties adequate for end uses such as in disposable diapers.
Accordingly, Tietz invented useful novel polyesters consisting essentially of recurring structural units of the formula EQU --C(O)--R--C(O)--OGO--
wherein R is
about 97 to 99.9 mole % para-phenylene (abbreviation T) and
about 0.1 to 3 mole % of a sulfonate radical (abbreviation 5SI) ##STR1## where M is an alkali metal or alkaline earth metal, and wherein G is
about 60 to 80 mole % --CH.sub.2 --CH.sub.2 --(abbreviation 2G) and
about 20 to 40 mole % --(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 --(abbreviation DEG),
and especially wherein R is about 98 mole % para-phenylene (T) and about 2% of the sulfonate radical (5SI) and G is about 80 mole % --CH.sub.2 --CH.sub.2 -- (2G) and about 20 mole % --(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 -- (DEG), and fibers, non-woven sheet, films and combinations thereof, and disposable diapers comprising such materials. Such polyesters are useful for some end uses, e.g., as described by Tietz. For other end uses, however, it would be desirable to provide degradable materials having properties better adapted for such different end uses. In particular, it is desirable to provide polyesters that can be formed into films that have still further improved toughness, but with similar advantageous properties in many respects, as regards the polyesters that have been specifically disclosed by Tietz.